Bright and efficient organic light-emitting diode (OLED) devices and electroluminescent (EL) devices have attracted considerable interest due to their potential application for flat panel displays (e.g., television and computer monitors) and lighting. OLED based displays offer advantages over the traditional liquid crystal displays, such as: wide viewing angle, fast response, lower power consumption, and lower cost. However, several challenges still must be addressed before OLEDs become truly affordable and attractive for next generation display and lighting. To realize white lighting and other full color display applications, it is essential to have the three fundamental colors of red, green, and blue provided by emitters with sufficient color purity and sufficiently high emission efficiency.
Phosphorescent Organic Light-Emitting Diodes (PhOLEDs) have recently received much attention because of their high energy efficiency for next generation flat panel displays and solid state lighting devices. OLEDs based on phosphorescent emitters can have three to four-fold higher device quantum efficiencies than those based on fluorescent emitters. The key challenge in PhOLEDs research is the development of phosphorescent metal complexes with high quantum efficiency and high stability, especially blue phosphorescent compounds. Phosphorescent compounds are among the most sought-after materials by industry around the world as one of the key color components for electroluminescent devices. Blue PhOLEDs based on Pt(II) compounds are rare and only a few examples are known (K. Li, et al., Chem. Commun., 2011, 47, 9075; Y. Unger, et al., Angew. Chem. Int. Ed., 2010, 49, 10214; E. L. Williams et al., Adv. Mater. 2007, 19, 197; M. Cocchi, et al., Appl. Phys. Lett. 2009, 94, 073309; M. Cocchi, et al., Adv. Funct. Mater., 2007, 17, 285; X. Yang et al., Adv. Mater. 2008, 20, 2405; S.-Y. Chang et al., Inorg. Chem. 2007, 46, 11202). Up to now, only a few examples of deep blue phosphorescent Pt(II) complexes with Commission internationale de L'Eclairage (CIE) coordinates near deep blue (0.15, 0.15) have been reported in the literature. Hence, there exists a need for blue phosphorescent compounds.